1. Field of the Invention
The present invention relates to a flat panel type display apparatus adapted to display an image in such a manner that electrons are made to be emitted from electron-emitting devices provided in a rear substrate, and phosphor layers provided in a front substrate is excited by the electrons to emit light.
2. Description of the Related Art
In recent years, a field emission display (FED), a display apparatus including surface conduction type electron-emitting devices, and the like, have been known as flat panel type display apparatuses having a vacuum envelope of a flat panel structure.
The FED and the display apparatus including surface conduction type electron-emitting devices have a vacuum envelope in which peripheral portions of front and rear substrates arranged opposite to each other at a predetermined interval via spacers are joined by a rectangular frame-like side wall, and the inside of which is evacuated.
Phosphor layers of three colors and a metal back covering the phosphor layers are formed over the inner surface of the front substrate. On the inner surface of the rear substrate, a number of electron-emitting devices as electron emission sources to make the phosphor layer excited and emit light, are arranged in correspondence with each pixel of the phosphor layer. Further, a getter film is formed over the inner surface of the front substrate in order to maintain a high vacuum inside the vacuum envelope.
A voltage higher by several kilovolts than the voltage of the electron-emitting device is applied to the metal back and the getter film, so that an electron beam emitted from the each electron-emitting device is accelerated by the electric field. Then, the accelerated electron beam passes through the metal back and the getter film, so as to be irradiated to the corresponding phosphor layer. Thereby, the phosphor is excited and emits light so as to display a color picture.
In this way, when the high voltage for accelerating the electron beam is applied between the front substrate and the rear substrate which are close to each other, a problem of discharge often arises. When the discharge is caused, a large current flows through the discharge place, so as to result in a problem that the electron-emitting device is damaged in the discharge place.
As a method for solving the problem, there is known a technique to reduce the discharge damage by such a way that the metal back covering the phosphor layer of the front substrate is electrically divided into small regions, and the resistance between the divided regions is made high, so that the current flowing at the time of the discharge is limited to reduce the discharge damage (see Japanese Patent Application Laid-Open No. H10-326583 and Japanese Patent Application Laid-Open No. 2000-311642). Further, there is known a technique adapted to divide the metal back layer and the getter layer, which are formed by vapor deposition, by reversely tapered ribs having the upper surface wider than the lower surface, in order to stabilize the resistance value between the divided regions of the metal back (see Japanese Patent Application Laid-Open No. 2006-073248). Further, there is disclosed a form in Japanese Patent Application Laid-Open No. H10-326583 and Japanese Patent Application Laid-Open No. 2000-311642, in which an anode is connected to an electrode via a resistor.
The present inventors have been investigating a structure for supplying an anode voltage to the anode via a resistor member from the electrode. Further, the present inventors have specifically investigated a structure in which the resistor member at least partially overlaps with the anode. As a result of the investigation, the present inventors have found a phenomenon that the resistance value between the electrode and the anode depends on the size of the anode forming region. The resistor member is used to prevent the state where the anode and the electrode is electrically connected to each other in a low resistance state. However, when the overlap between the resistor member and the anode is large, a desired resistance can be no longer obtained. An object of the present invention is to provide a display apparatus capable of realizing a suitable resistance state in the structure in which the anode and the electrode are connected to each other via a resistor member. One of specific examples resulting from the object will be described below.
An electroconductive layer which functions as an anode such as a metal back or a getter, may be formed in an image display area. Thus, it is possible restrict the film forming range of the electroconductive layer to the image display area by providing a guide at the time when an electroconductive material is irradiated, or by irradiating the electroconductive material in a box. However, structures on a substrate are damaged when the guide and the box are brought into contact with the substrate. Thus, it is preferred that the guide and the box are disposed at a distance from the substrate. However, when the electroconductive material is irradiated in the state where the guide and the box are disposed in this way, an electroconductive layer is also formed outside the image display area by the electroconductive material irradiated through a gap between the guide and the substrate, or through a gap between the box and the substrate.
In the periphery of the electroconductive layer formed in the image display area of the front substrate, a common electrode is annularly provided so as to surround the periphery of the electroconductive layer. The electroconductive layer and the common electrode are connected via a plurality of connecting resistors. The connecting resistor has a function to suppress a current which when an abnormal discharge is caused in the image display area, flows into the electroconductive layer from the common electrode for supplying electric power to the electroconductive layer in a high voltage.
However, when the electroconductive layer is formed outside the image display area as described above, the electroconductive layer is also formed on the connecting resistor, so that the length of the portion which functions as the connecting resistor is shortened to reduce the resistance value between the common electrode and the electroconductive layer. As a result, the connecting resistor is unable to suppress the current flowing into the electroconductive layer from the common electrode at the time when the abnormal discharge occurs in the image display area. The edge position of the region forming the electroconductive layer cannot be strictly fixed due to the characteristic of the electroconductive layer forming process as described above. Therefore, the resistance value between the common electrode and the electroconductive layer is made different depending on the forming region of the electroconductive layer on the connecting resistor.